What are the pKa values of C–H bonds in aromatic heterocyclic compounds in DMSO?

Charge density analysis from both experimental and theoretical points of view on two molecular complexes: one is formed between nicotinamide and salicylic acid, and the other formed between nicotinamide and oxalic acid brings out the quantitative topological features to distinguish a cocrystal from a salt.

Charge Density Analysis of Crystals of Nicotinamide with Salicylic Acid and Oxalic Acid: An Insight into the Salt to Cocrystal Continuum

1 An Overview of the Development of Nonequilibrium Solvation Theory 908 2 The Correct Way for Integration of Free Energy Change 925 2.1 Problems of path-dependent expression of free energy . . . . . . . . 925 2.2 Correct integration method . . . . . . . . . . . . . . . . . . . . . . . 931 2.3 Field superposition approach . . . . . . . . . . . . . . . . . . . . . . 935 2.4 Electrostatic free energy in electric field-displacement form . . . . . 935 3 Interaction Energy between Solvent Polarization and Solute Charge 937 3.1 Energy in a dielectric system: A microscopic description . . . . . . . 937 3.1.1 Charging work of free charge and bound charge . . . . . . . . 937 3.1.2 “Spring” energy . . . . . . . . . . . . . . . . . . . . . . . . . 941 3.2 Energy in a dielectric system: A macroscopic description . . . . . . . 945 3.2.1 Self-energy of a polarization field . . . . . . . . . . . . . . . . 945 3.2.2 An example of zero self-energy of a polarization field . . . . . 948 4 Analytical Expression for Solvent Reorganization Energy and Spectral Shift 950 4.1 Solvent effect for electron transfer . . . . . . . . . . . . . . . . . . . . 950

Continuous medium theory for nonequilibrium solvation: new formulations and an overview of theories and applications

We investigate the structures, NMR chemical shifts, absorption spectra, frontier molecular orbitals, and transition density matrices of π-stacked polyfluorenes by ab initio calculations. For F1−F4, we consider two different conformations, syn and anti. The simulated 1H NMR chemical shifts are in good agreement with the previous experiment, and the significantly upfielded chemical shifts explain that the fluorene moieties are stacked on each other. It is found that the relative stability for syn and anti conformers is almost equivalent in B3LYP calculations; however, the syn conformer becomes much more stable than the anti conformer in MP2 calculations, which is consistent with the experimental finding that only the syn conformers are relevant. The vertical detachment energy, which is linearly proportional to the ionization potential, shows the same size dependence as the previous experiment. The electron attachment energy decreases exponentially as the size increases, which implies that the electron trans...

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Stacking Effect of Polyfluorene on the Chemical Shift and Electron Transport

The evolution of the electronic first-order longitudinal hyperpolarizability (βzzz) and the hyperpolarizability aligned along the direction of the dipole moment (βμ) of the α-helix and β-strand single chain H2N–(CH2–CO–NH)n–CH2–COOH (n = 1–9) oligoglycines, were investigated. For this purpose we have used Hartree–Fock, second-order Moller–Plesset perturbation theory and Coulomb-attenuating Density Functional Theory computations. For the longest chain, βμ(β-strand) is one order of magnitude greater than βμ(α-helix), due to the cooperative effect of the α-helices being unfavourable for the NLO properties. The βzzz and βμ values per unit cell of the β-strand conformation were determined, extrapolating the properties in the limit of the polymer. The calculated βzzz values were elucidated using the two-state model involving the characteristic π–π* NV1 electronic transition of peptides. Single chain β-strand polyglycines can be discriminated from the α-helices using second-order NLO effects.

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The effect of secondary structures on the NLO properties of single chain oligopeptides: a comparison between β-strand and α-helix polyglycines.

Using ab initio and density functional calculations, we studied photoexcitation of a charge-balanced electron donor–acceptor (DA) complex comprised of tetracyanoethylene (TCE) and tetramethylethylene (TME). We considered both the TCE-TME stacked conformer and a possible conformer with a solvent molecule (dichloromethane) inserted between TCE and TME. The photoexcitation of the DA complex can directly form a charge transfer (CT) state. Our theoretical investigations show that the CT state can also be produced from the decay of higher excited states. Using the continuum model, we investigated the solvent effects on CT absorption, local excitation, and CT emission in the polar solvent. The equilibrium solvation energies of the ground and excited states of the DA complex were calculated using the self-consistent reaction field method, and then the correction of nonequilibrium solvation energies for the vertical transitions was made. The transition energies (i.e., CT absorption for the DA complexes and CT emis...

Theoretical study of photoinduced electron transfer from tetramethylethylene to tetracyanoethylene

Ab initio calculations were performed to investigate the charge separation and charge recombination processes in the photoinduced electron transfer reaction between tetracyanoethylene and acenaphthylene. The excited states of the charge-balanced electron donor–acceptor complex and the singlet state of ion pair complex were studied by employing configuration interaction singles method. The equilibrium geometry of electron donor–acceptor complex was obtained by the second-order Moller–Plesset method, with the interaction energy corrected by the counterpoise method. The theoretical study of ground state and excited states of electron donor–acceptor complex in this work reveals that the S1 and S2 states of the electron donor–acceptor complexes are excited charge transfer states, and charge transfer absorptions that corresponds to the S0 S1 and S0 S2 transitions arise from π–π* excitations. The charge recombination in the ion pair complex will produce the charge-balanced ground state or excited triplet state. According to the generalized Mulliken–Hush model, the electron coupling matrix elements of the charge separation process and the charge recombination process were obtained. Based on the continuum model, charge transfer absorption and charge transfer emission in the polar solvent of 1,2-dichloroethane were investigated. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 94: 23–35, 2003

Xiao-Hui Duan

Papers

Theoretical study of photoinduced electron transfer from tetramethylethylene to tetracyanoethylene

Theoretical investigation of charge transfer excitation and charge recombination in acenaphthylene–tetracyanoethylene complex